1. Field of the Invention
The present invention relates to a hand lever device for operating a drive member, such as a throttle valve, of an internal combustion engine via a cable. In particular, the hand lever is preferably mounted on a working machine, such as a hedge trimmer or brush cutter, in the vicinity of a hand grip so that it is easy and convenient to operate such a throttle valve or the like via a throttle cable or the like.
2. Description of the Prior Art
For example, in a working machine such as a hedge trimmer and brush cutter, which includes an operative device such as a cutting blade or the like driven by an internal combustion engine, a hand lever device for controlling engine speed has been provided for controlling the degree of opening of a throttle valve of the internal combustion engine. Such hand levers have been mounted in the vicinity of a grip of a U-shaped handle, a bar handle or the like of the working machine so as to provide manual control of the output force of the internal combustion engine.
The hand lever device is generally provided with a throttle trigger (throttle lever) operated by the operator's fingers and adapted to be pivotally operated to thereby control the degree of opening of the throttle valve via a throttle cable. In general, the throttle valve is always biased toward the direction of minimum opening for an idle condition. Accordingly, the throttle valve is normally kept at the idle opening degree for an idle speed and, when the throttle cable is drawn, it begins to open the throttle from that idle opening position toward an opening position for higher speed operation.
Such hand lever devices for controlling throttle valve settings have been known to include an automatic return to an idle type arrangement. Consequently, when such a throttle lever is released from a pivotally operated position, the lever is automatically returned to its original idle position setting thereby moving the throttle valve to its idle setting. Conversely, such a hand lever could be of an immobilizable type such that when fingers are released from a throttle lever, the throttle lever will be held immobilized at a desired pivotally operated position (see Japanese Examined Utility Model Publication No. 19944/1982, etc.).
In the auto-return type, when fingers are released from the throttle lever, the engine is automatically returned to an idling condition. Consequently, when the auto-return type is used in a working machine, where the output force of the engine is transmitted to an operative portion including a cutting blade via a centrifugal clutch, the centrifugal clutch is disconnected to cut off the transmission of the driving force to the operative portion. Accordingly, the operation of the machinery can immediately be stopped by returning the throttle valve to the opening degree for idle rotation if an accident occurs, thereby advantageously attaining improved safety. On the other hand, the throttle valve must be held continuously by fingers at a desired pivotally operated position to achieve desired operation of the machinery. This causes problems in that this type is awkward with respect to intermediate opening degrees, the fingers remain susceptible to fatigue, and the speed of the engine is likely to be unstable.
In contrast thereto, the immobilizable type is capable of solving the above problems associated with the auto-return to idle rotation opening degree type. The immobilization type advantageously holds the throttle lever at a desired pivotally operated position without being held by the operator's fingers. That operation is preferred because the fingers are liberated from holding it. However, since additional operation is required to release the throttle lever from the immobilization position, it is impossible to immediately stop the machinery even if an accident occurs. Accordingly, there is a problem that, in terms of safety, the immobilizable type is inferior to the auto-return to idle rotation opening degree type.